Three decades of longlining in Bimini, Bahamas, reveals long‐term trends in lemon shark Negaprion brevirostris (Carcharhinidae) catch per unit effort

Abstract

In Bimini, Bahamas, the consistent employment of longlines, beginning in 1982, provided a rare opportunity to explore population trends for large resident sharks. This study assessed three shallow water longline survey periods at this location; 1982–1989, 1992–2002 and 2003–2014, with the aim of determining trends in annual catch per unit effort ( CPUE ) for an IUCN listed near‐threatened species, the lemon shark Negaprion brevirostris . A general additive model ( GAM ) was used to analyse the non‐linear annual CPUE values over the entire 32‐year research period. The GAM displayed high variability of annual CPUE , with a peak value of 0·026 N. brevirostris per hook day (hooks day −1 ) in 2000. The temporal pattern of CPUE indicated an abundance trend with a complete cycle, from trough to trough, occurring over a period of approximately 18 years. The 1982–1989 survey period saw the highest proportion of mature individuals (19·8%) and the smallest average pre‐caudal length ( L PC ; 124·8 cm). The 1992–2002 survey period had the highest average annual CPUE (0·018 hooks day −1 ), while the 2003–2014 research period saw largest average L PC size (134·8 cm) and the lowest average CPUE values (0·009 hooks day −1 ) of the entire research period. The long‐term trend identified in this study provides a baseline for future assessment.

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